1. Field of the Invention
The present invention relates to a writing implement, and particularly to a writing implement in which ink and a follower advancing with consumption of the ink are stored directly inside a barrel having a pen point at its forward end.
2. Description of the Related Art
In such a conventional writing implement, ink and a follower are stored in a barrel directly, and a tail plug (corresponding to an inner tail plug in the present invention) having a ventilating means is fitted to the inner surface of a rear end aperture portion of the barrel, as disclosed, for example, in Unexamined Japanese Patent Publication (kokai) No. Hei 6-115291.
Particularly, in such a writing implement in which ink and a follower are stored in a barrel directly, while a large volume of ink can be stored, the ink is apt to flow back (that is, go down) by the own weight of the large volume of ink when the pen point is directed upward. Therefore, in the conventional writing implement, a back-flow valve system constituted by a ball valve actuated by the own weight of a ball valve (generally a metallic ball) is provided in the tail plug in order to prevent the ink from flowing back when the pen point is directed upward.
However, in the conventional writing implement, since an air hole is formed at the rear end of the tail plug, dust or dirt is apt to enter the air hole of the tail plug from the outside. Therefore, there is a fear of hampering the valve function of the back-flow valve system. If the back-flow valve system cannot operate normally, there is a fear that ink leaks directly to the outside through the air hole. Further, if the writing implement is put into a pocket of clothes at that time, the leaking ink will make the clothes dirty. That is, conventionally, such a writing implement does not have any safety measures against failure in operation of the back-flow valve system. Therefore, there is a fear that an accident of ink leaking from the rear end of the writing implement occurs.